JP2018527451A - Polymer gel, method for producing the same, and use thereof - Google Patents

Abstract

The present invention relates to a method for producing a polymer comprising a step of crosslinking a polymer by using a cyclic dianhydride of a carboxylic acid as a crosslinking agent, and a step of treating a polymer gel with a bicarbonate. The invention further relates to the polymer gels obtained by the method of the invention and their use in various applications.

Description

  The present invention relates to a polymer gel and a method for producing the same.

  A polymer gel is a cross-linked polymer that can absorb a large amount of liquid, such as water. In particular, a crosslinked polymer hydrogel capable of absorbing an amount of water exceeding 10 times its dry weight is defined as a “superabsorbent”. Cross-links or cross-linking knots, ie physical or chemical bonds between the polymer chains forming the polymer network, ensure the structural integrity of the polymer-liquid system, On the one hand, the complete solubility of the polymer is inhibited, and on the other hand it is possible to maintain a liquid phase within the molecular mesh.

  Currently marketed polymer gels are characterized by their biocompatibility due to their remarkable absorption properties as well as possibly due to their high water content and in particular their ability to adjust their absorption properties in response to external stimuli. It is done. As a result, such polymer hydrogels can be used as intelligent materials, for example for the manufacture of sensors or actuators for a number of industrial applications. Besides the usual use as an absorbent core in the field of personal hygiene absorbent products, for example in the biomedical field, for the development of controlled-release pharmaceutical preparations, artificial muscles, sensors etc. and in agriculture and horticulture, for example There are more modern and innovative applications in devices for the controlled release of water and nutrients in dry soils.

However, currently available polymer gels are mostly acrylic products and are therefore not biodegradable.
In recent years, due to increasing interest in environmental protection issues, there has been great interest in developing superabsorbent materials based on biodegradable polymers that have similar properties to traditional superabsorbent polyacrylic acid. Gathered.
Examples of biodegradable polymers used to obtain superabsorbent polymer gels are starch and cellulose derivatives.

  In 1990, Ambergen U and Oppermann W, Polymer, 31, 1854 proposed a method of synthesizing superabsorbent materials made entirely from cellulose derivatives. In particular, hydroxyethylcellulose (HEC) and carboxymethylcellulose sodium salt (CMCNa) chemically crosslinked in basic solution with divinylsulfone were used. However, the absorption characteristics of such materials are not as high as those of acrylic superabsorbent materials.

  Some carbodiimides are also known among unconventional crosslinkers. In particular, the use of carbodiimides to cross-link chlorinated or non-chlorinated carboxymethylcellulose (CMC) is described in Spanish Patent No. 484964 and WO 2006/070337. However, during the cross-linking reaction with CMCNa, this material turns into a slightly toxic urea derivative, which must be removed during the washing process, thereby further increasing the cost and complexity of the production process.

  More recently, US 2010/0234233 describes the use of polycarboxylic acids such as citric acid as cross-linking agents to produce hydrogels. The polymer used herein is a mixture of ionic and nonionic polymers, such as a mixture of carboxymethyl cellulose and hydroxyethyl cellulose. Molecular spacers that are polyhydroxyl alcohols such as sorbitol have also been disclosed as being useful for increasing the absorption capacity of hydrogels. This method works with hydrophilic polymers. However, in the case of a hydrophobic polymer such as cellulose acetate, the swelling ratio obtained by this method is not satisfactory.

Spanish Patent No. 484964 International Publication No. 2006/070337 US Patent Application Publication No. 2010/0234233

By Ambergen U and Oppermann W, Polymer, 31, 1854

  The object of the present invention is to provide a novel polymer gel that overcomes the above disadvantages, is biodegradable, is environmentally friendly and has high swellability.

These and other objects are achieved by the polymer gels of the present invention and the manufacturing methods defined herein.
The polymer gel of the present invention is obtained by a crosslinking reaction with a cyclic dianhydride and a treatment with a bicarbonate solution. Advantageously, the polymer reaction is carried out with a cyclic monoanhydride which acts as a polar molecular spacer before crosslinking.

The present invention finds that crosslinking of a cellulose derivative previously reacted with a specific monoanhydride with a specific dianhydride, such as pyromellitic dianhydride, results in the formation of a polymer gel with high liquid absorption capacity. Partly related to Pyromellitic dianhydride is disclosed in US 2010/0234233 and in the article Quim. Nova, Vol. 36,
No. 1,02-106, 2013 is reported as a crosslinker for polymers such as cellulose derivatives, but the combination with subsequent treatment with a bicarbonate solution has not yet been disclosed. Also, a combination of a cyclic monoanhydride and a pre-reacted polymer is not disclosed.

In this context, the process for producing the polymer gel of the invention
(A) adding a cyclic dianhydride to a solution containing the polymer in the presence of a catalyst; and (b) maintaining the solution of step (a) under conditions suitable for crosslinking of the hydrophilic polymer with the cyclic dianhydride. Forming a polymer gel thereby,
(C) including a step of treating the polymer gel with an aqueous bicarbonate solution.

In yet another embodiment, the present invention provides a polymer gel that can be produced using the methods of the present invention.
Such polymer gels comprise a polymer matrix containing polymer chains with hydroxy-pending groups, the first part of the hydroxy-pending groups cross-links the polymer chains together and has polar functional COOH and / or salts thereof Substituted by a divalent hydrocarbon group (derived from a cyclic dianhydride). The second portion of the hydroxy-pending group is substituted with a monovalent hydrocarbon group (derived from a cyclic monoanhydride), and the monovalent hydrocarbon group contains a polar functional COOH and / or a salt thereof. It is advantageous to have.

By “first part” it is understood that this part represents 10-70% of the total number of free OH groups of pending hydroxyl groups in the polymer.
By “second part” it is understood that this part represents 10-70% of the total number of free OH groups of pending hydroxyl groups in the polymer before reaction with the monoanhydride.

  Furthermore, the present invention includes products comprising such polymer gels.

<Definition>
The term “biological source” means a material derived from a renewable resource. Renewable resources are natural resources, animal resources or plant resources, and the resource reserve can be reconstructed in a short time on a human time scale. In particular, this reserve needs to be reproducible as quickly as it is consumed.
Unlike materials derived from fossil materials, renewable starting materials contain a high proportion of ¹⁴ C. This feature can be revealed through one of the methods described in standard ASTM D6866, in particular according to mass spectrometry or liquid scintillation spectroscopy.
These renewable resources are generally cultivated or non-cultivated plant materials such as wood, plants such as sugarcane, corn, cassava, wheat, rapeseed, sunflower, or castor oil, or fat (fat Etc.).

  The terms “anhydride”, “monoanhydride” and “dianhydride” mean herein “carboxylic anhydride”, “carboxylic monoanhydride” and “carboxylic dianhydride”.

  The term “a” is in the general plural and should be understood as “one or more” unless explicitly stated otherwise.

  As used herein, the term “polymer” may mean a homopolymer comprising one repeating unit or a copolymer comprising two or more different repeating units.

  The present invention provides polymer gels, methods for making polymer gels, methods for using polymer gels, and products comprising polymer gels.

The method for producing the polymer gel of the present invention comprises:
(A) adding a cyclic dianhydride to a solution containing the polymer in the presence of a catalyst; and (b) maintaining the solution of step (a) under conditions suitable for crosslinking of the hydrophilic polymer with the cyclic dianhydride. And thereby forming a polymer gel,
(C) including a step of treating the polymer gel with an aqueous bicarbonate solution.
Advantageously, the method of the invention further comprises a step (a0) of adding a cyclic monoanhydride to a solution containing a polymer containing hydroxyl groups in the presence of a catalyst prior to step (a).

<Polymer and solution containing polymer>
In the process of the invention, the polymer is advantageously selected from the group consisting of polysaccharides and their derivatives.

  Examples of suitable polysaccharides include cellulose, hemicellulose, substituted cellulose, substituted dextran, substituted starch, glycosaminoglycan and polyuronic acid, alginate, and mixtures thereof.

  The polysaccharides that can be used are methylcellulose, ethylcellulose, n-propylcellulose, hydroxyethylcellulose, hydroxy-n-propylcellulose, hydroxy-n-butylcellulose, hyoxyxypropylmethylcellulose, ethylhydroxyethylcellulose, cellulose, hemicellulose, Cellulose acetate (mono, di, or tri, or a mixture thereof), cellulose propionate (mono, di, or tri, or a mixture thereof), carboxymethyl cellulose, carboxymethyl starch, dextran sulfate, dextran phosphate, diethylaminodextran, heparin , Hyaluronic acid, chondroitin, chondroitin sulfate, heparan sulfate, polyglucuronic acid, polymanuronic acid, Galacturonic acid is selected from the group consisting of Poriarabin acid and mixtures thereof.

  In a preferred embodiment, the polymer is cellulose, hemicellulose, cellulose acetate (mono, di, or tri, or a mixture thereof), cellulose propionate (mono, di, or tri, or a mixture thereof), carboxymethyl cellulose and their Selected from the list of mixtures. If cellulose triacetate is used, it is in a mixture with cellulose monoacetate and / or cellulose diacetate.

  Advantageously, the polymer is cellulose acetate having a degree of substitution of OH groups of 1 to 3, preferably 1.3 to 3, more preferably 2.2 to 2.7.

  In certain embodiments, the polymer is a biological source based on the standard ASTM D6866 described above.

  In the method of the present invention, the polymer-containing solution is advantageously an organic solvent-based solution, and the organic solvent is selected from the following list: acetone, dimethyl sulfoxide, aniline, benzyl alcohol, cyclohexanone, diethanolamine, N, N- Dimethylacetamide, dimethylformamide, 1,5-dimethyl-2-pyrrolidone, 1,4-dioxane, ethylene glycol ether, ethyl acetate, hexafluoroisopropanol, methyl acetate, n-methylpyrrolidone-2, naphthol, pyridine, tetrafluoro- n-propanol, tetrafluoroisopropanol, trifluoroethanol, and mixtures thereof. Preferably acetone is selected.

  In a preferred embodiment, the polymer is about 2% to 30%, preferably about 8% to 20% by weight of the total weight of the solution before adding the cyclic dianhydride (or before adding the cyclic dianhydride). Present in a concentration by weight.

<Cyclic dianhydride>
The cyclic dianhydride of the present invention includes pyromellitic dianhydride (PMDA), ethylenediaminetetraacetic acid dianhydride (EDTA), diethylenetriaminepentaacetic dianhydride (DTPA), 3,3 ′, 4,4′-bis. It may be selected from the group consisting of phenyltetracarboxylic dianhydride (BPDA), pyromellitic diimide (PyDi), benzophenone-3,3 ′, 4,4′-tetracarboxylic dianhydride and mixtures thereof.
Pyromellitic dianhydride (PDMA) is preferred.

  The dianhydride is advantageously dissolved in an organic solvent-based solution, the organic solvent being selected in the list: acetone, dimethyl sulfoxide, aniline, benzyl alcohol, cyclohexanone, diethanolamine, N, N-dimethyl. Acetamide, dimethylformamide, 1,5-dimethyl-2-pyrrolidone, 1,4-dioxane, ethylene glycol ether, ethyl acetate, hexafluoroisopropanol, methyl acetate, n-methylpyrrolidone-2, naphthol, pyridine, tetrafluoro-n -Propanol, tetrafluoroisopropanol, trifluoroethanol and mixtures thereof. Preferably acetone is selected.

<Cyclic monoanhydride>
The process of the present invention comprises cycloaliphatic anhydrides such as maleic anhydride and succinic anhydride, or aromatic anhydrides such as phthalic anhydride and 1,2,4-benzenetricarboxylic anhydride, and Cyclic monoanhydrides that can be selected from the group consisting of mixtures thereof can be used. Preferably, the cyclic monoanhydride is phthalic anhydride.

  The reaction of the cyclic monoanhydride increases the absorbency of the final polymer gel. Cyclic monoanhydrides act as polar molecular spacers by sterically blocking access to polymer chains, thereby increasing the average distance between polymer chains and attracting polar molecules such as water. Thus, cross-linking can occur at sites that are not close to each other or systematically present at all OH positions, thereby increasing the ability of the polymer network to expand to greatly increase the polymer hydrogel absorption properties.

  The best results with respect to swellability are obtained when the monoanhydride is phthalic anhydride and the dianhydride is pyromellitic dianhydride (PDMA).

<Conditions>
(concentration)
In the process of the invention, in the solution of step (a0), the exact molar ratio of monoanhydride per hydroxyl group of the polymer is about 0.1-1 mol / mol, preferably 0.25-1 mol / mol. More preferably 0.5 to 1 mol / mol and especially 0.75 mol / mol.

  Also, in the solution of step (a), the molar ratio of dianhydride per hydroxyl group of the polymer is preferably about 0.1 to 2 mol / mol, preferably 0.5 to 1.5 mol / mol, more Preferably it is 0.75 to 1.25 mol / mol, and in particular 1 mol / mol.

  These molar ratios are determined before the reaction with the cyclic dianhydride when no monoanhydride is used, or before the reaction with the cyclic monoanhydride when a cyclic monoanhydride is used. Calculated by content.

  The best result is that the molar ratio of monoanhydride per hydroxyl group of the polymer in the solution of step (a0) is about 0.5-1 mol / mol, and per hydroxyl group of the polymer in the solution of step (a) Is obtained when the dianhydride molar ratio is preferably about 0.75 to 1.25 mol / mol. More preferably, the molar ratio of monoanhydride per polymer hydroxy group in the solution of step (a0) is 0.75 mol / mol, and the mole of dianhydride per hydroxyl group of polymer in the solution of step (a). The ratio is 1 mol / mol.

(Temperature, pressure)
In certain embodiments of the method of the present invention, the polymer is heated to an organic solvent prior to step (a0) at a temperature of about 10 to 150 ° C, preferably 10 to 50 ° C, more preferably 15 to 30 ° C, more preferably. Dissolved at room temperature. The pressure should be maintained above the system vapor pressure. The pressure in the dissolution process can be selected from 0.5 to 1.5 bar, but is advantageously atmospheric.

During step (a0), the solution is advantageously maintained at a temperature of about 30-90 ° C, preferably about 50-80 ° C, more preferably about 50-60 ° C. The pressure in step (a0) is advantageously atmospheric even if selected at 0.5 to 1.5 bar.
The temperature and reaction time are controlled to allow a sufficient number of OH functional groups of the polymer to react with the monoanhydride. The reaction time is generally 1 to 6 hours.
This step (a0) aims at obtaining a partially OH-substituted polymer, preferably the portion of free OH groups substituted by monoanhydride is free OH of the polymer before adding monoanhydride. It is 10% to 70% of the total number of groups.

Then, during step (a), preferably the solution is maintained at a temperature of about 10-90 ° C, preferably about 15-50 ° C, more preferably at room temperature. The pressure in step (a) is advantageously atmospheric even if 0.5 to 1.5 bar is selected.
The addition of dianhydride in step (a) can be very fast and is generally less than 10 minutes.

  In an embodiment of the method of the present invention, during step (b), the solution is maintained at a temperature of about 10-50 ° C, preferably about 15-40 ° C, more preferably at room temperature. The temperature of step (b) should not be higher than the boiling point of the solvent used to dissolve the polymer and / or dianhydride. When the gel is formed, the crosslinking reaction is generally stopped. This may correspond to a reaction time in step (c) plus (b) of less than 24 hours, in particular less than 3 hours, more preferably less than 30 minutes.

  In the method of the present invention, the catalyst in step (a) and / or step (a0) is preferably a basic catalyst and is selected from the group consisting of pyridine, triethylamine, DMAP (dimethylamine pyridine) and mixtures thereof. It is advantageous.

<Further process>
In the method, the polymer gel is washed with a polar organic solvent such as water, methanol or ethanol, or a combination thereof during the step of purifying the polymer gel, for example, step (b) and step (c). Step (b1) can be further included.
A polymer gel immersed in a polar solvent swells and releases optional components such as by-products or unreacted monoanhydrides, dianhydrides that are not incorporated into the polymer network. Water is preferred as the polar solvent, and distilled water is more preferred. The volume of water required to achieve the maximum degree of swelling of the gel during this step is about 10-20 times greater than the initial volume of the gel. The step of washing the polymer gel by arbitrarily changing the polar solvent to be used may be repeated a plurality of times. For example, the polymer gel is washed with distilled water followed by methanol or ethanol, and these two steps are optionally repeated multiple times.

The method can further include a step (b2) of drying the washed polymer gel before step (c) and after step (b1).
The drying step (b2) can include a step of immersing the washed polymer gel in a cellulose non-solvent.

  In this case, it is carried out by a step of immersing the completely swollen polymer gel in a cellulose non-solvent. This method is known as phase inversion. Suitable cellulose non-solvents include, for example, acetone and ethanol. The process of drying the polymer gel by phase inversion results in a final porous structure that improves the absorption properties of the polymer gel by capillary action. Furthermore, when the pores are interconnected or open, i.e. the micropores are in communication with each other, the gel absorption / desorption rate is also improved. When a fully or partially swollen gel is immersed in a non-solvent, the gel undergoes phase inversion with drainage of water until it precipitates as white particles in a glassy solid form. In order to obtain a dried gel in a short time, various rinses in a non-solvent may be necessary. For example, when a swollen polymer gel is immersed in acetone as a non-solvent, a water / acetone mixture is formed that increases in water content as the polymer gel dries. At certain acetone / water concentrations, eg, about 55 percent in acetone, water cannot exit the polymer gel and therefore fresh acetone must be added to the polymer gel in order to proceed with the drying process. Increasing the acetone / water ratio during drying speeds up the drying process. The pore size is affected by the speed of the drying process and the initial size of the polymer gel particles. Larger particles and faster processes tend to increase pore size. Pore sizes in the microscale range are preferred because pores in this size range exhibit a strong capillary effect and provide higher absorption and water retention capabilities.

  The polymer gel of the present invention may be dried in step (b2) by other methods such as air drying, freeze drying, or oven drying. These drying methods can be used alone, in combination, or in combination with the above non-solvent drying steps. For example, the polymer gel can be dried in a non-solvent following air drying, lyophilization, oven drying, or a combination thereof to remove any residual non-solvent. Oven drying can be performed at a temperature of about 30-45 ° C. until residual non-solvent is completely removed. The washed and dried polymer gel can be used as is or can be pulverized to produce a polymer gel of the desired size.

  Step (b2) is advantageously a step of drying the washed polymer gel by oven drying, preferably at a temperature of about 40 ° C.

In the method of the present invention, the step (c) of treating the polymer gel with an aqueous bicarbonate solution such as sodium bicarbonate or potassium bicarbonate is performed.
The aqueous bicarbonate solution is advantageously a saturated solution of sodium bicarbonate or potassium bicarbonate.
Step (c) of treating the polymer with a bicarbonate solution has the advantage of imparting more polarity to the gel and surprisingly increasing the swelling performance.

  It is recommended to further comprise step (d) of drying the polymer gel of step (c), for example in an oven or any of the drying methods described above, preferably at a temperature of about 40 ° C.

<Polymer gel>
By using the method of the present invention, the resulting polymer gel has a swelling ratio according to the ASTM JIS K 7223-teaback method of at least about 10, preferably at least about 50, more preferably at least about 100.

The present invention further comprises a product comprising the polymer gel of the present invention. Such products include, for example, consumer products such as personal care absorbent products (ie, infant napkins, sanitary napkins, etc.) and agricultural products (eg, devices with controlled release of water and nutrients). In which polyacrylic acid polymer hydrogels are conventionally used. Thus, the polymer hydrogel obtained by the method of the present invention has mechanical properties suitable for use in all of the above fields. Thus, the scope of the present invention is by the method of the present invention as an absorbent material in a product that can absorb water and / or aqueous solution and / or swell when in contact with water and / or aqueous solution. Including the use of the resulting polymer gel.
The polymer gels and superabsorbent polymer gels of the present invention can be used as absorbent materials in the following fields provided by non-limiting examples.

-Agricultural products (e.g., devices that have controlled release of water and / or nutrients and / or phytochemicals, especially in dry wastelands, and in all cases where frequent irrigation is impossible) Or such a product mixed with soil in the area surrounding the plant roots in swollen form can absorb and retain water during irrigation and release slowly with nutrients and phytochemicals useful for cultivation In);
In personal hygiene products and household absorbent products (such as absorbent cores such as baby napkins, sanitary napkins, etc.);
-The field of toys and machinery (eg products whose size can be significantly changed after contact with water or aqueous solutions)
The above products containing the polymer hydrogel of the present invention as an absorbent material are also within the scope of the present invention.

  In summary, the products of the present invention are preferably devices with controlled release of water, nutrients or phytochemicals in agriculture, devices for environmental remediation, absorbent products for personal and home hygiene, toys, and water. Or, when contacted with an aqueous solution, it is selected from the group consisting of devices adapted to change their size.

  The following examples further illustrate the invention but are not intended to limit its scope.

  The materials and methods of the present invention will be better understood in connection with the following examples. These examples are intended as illustrative only and do not limit the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art, and such changes and modifications include, but are not limited to, those relating to the chemical structures, derivatives, formulations, and / or methods of the present invention. Is not to be done. It is within the spirit of the invention and the scope of the appended claims.

Ｗ_０−乾燥ゲルの質量
Ｗ_１−ゲル無しでのバックの質量
Ｗ_２−バック及び膨潤ゲルの質量
で算出した。この方法の精度は、その製品により±３．５％程度と明らかにされている。
参照：ＡＳＴＭ：日本工業規格（ＪＩＳ）Ｋ ７２２３−ティーバック法 <I-swell test>
(ASTM standard for water swelling)
Swelling Test Teaback The swelling test is determined based on the teaback method. For this test, 200 mg (W _o ) of gel was weighed and placed in a steel bag having dimensions of 60 × 60 mm. The bag was immersed in water at room temperature for 24 hours. After this time had elapsed, excess water was removed by hanging the bank until no liquid dropped. The bag having the swollen gel is weighed (W ₂ ), and the swelling ratio (Se) is expressed by the formula:

W ₀ -Mass of dry gel W ₁ -Mass of bag without gel W ₂ -Calculated by the mass of bag and swollen gel. The accuracy of this method is clarified to be about ± 3.5% by the product.
Reference: ASTM: Japanese Industrial Standard (JIS) K 7223-Teaback method

<Reaction of cellulose acetate without monoanhydride (CA-DS2.5) and dianhydride (PMDA, EDTA, DTPA and BPDA)>
With mechanical stirring (400 rpm) for 2 hours at room temperature, 5 g CA-DS2.5 (9.35 × 10 ⁻³ mol free OH) in 50 g acetone (10% w / w) with a Becker. Dissolved. In a sealed becker, the dianhydride (0.5, 1.0 or 2.0 dianhydride: 1.0 polymer free OH, mol: mol) was added to the previous solution. After dissolving all dianhydrides over about 10 minutes, triethylamine as a catalyst (1.0 catalyst: 1.0 dianhydride, mol: mol) was added to the previous solution at a flow rate of about 2 mL / min. . The reaction was stopped when gel formation was observed. Finally, the gel was washed with a water / ethanol solution 20% v / v and dried in an oven at 40 ° C. overnight.
Each dianhydride was dissolved in a different solvent according to Table 1 below.

実施例１の結果を以下の表４に示す。

The results of Example 1 are shown in Table 4 below.

<Comparison-Reaction of cellulose acetate (CA-DS2.5) and monoanhydride (phthalic anhydride-PA) without dianhydride>
In a 250 mL capacity reaction vessel, 5 g CA-DS2.5 (9.35 × 10 ⁻³ mol free OH) was mechanically stirred in 50 g acetone (10% w / w) (400 rpm). It was dissolved at room temperature for 2 hours. Thereafter, the temperature of the system was raised to 56 ° C. When this temperature was reached, PA (0.25 or 0.75 PA: 1.0 polymer free OH, mole: mole) was added into the system. After dissolution (requires stirring for about 10 minutes), triethylamine (1.0 catalyst: 1.0 monoanhydride, mol: mol) as catalyst was added. After 4 hours of reaction, the system was cooled to room temperature and the product was precipitated with water. Finally, the product was washed with a water / ethanol solution (20% v / v) and dried in a 40 ° C. oven overnight.

二無水物を含まない生成物は、繊維状の外観を有し、水中にゲルを形成しない。外観は「綿」と似ており水を吸収するが、繊維状の形態で維持される。
二無水物を含まないこの場合、鎖は架橋を有していないためより移動性を有する。

The product without dianhydride has a fibrous appearance and does not form a gel in water. Appearance resembles “cotton” and absorbs water, but remains in a fibrous form.
In this case, which does not contain a dianhydride, the chain is more mobile because it has no crosslinks.

<3.1 Cellulose acetate (CA-DS2.5) and monoanhydride (reaction of phthalic anhydride PA)>
In a 250 mL capacity reaction vessel, 5 g CA-DS2.5 (9.35 × 10 ⁻³ mol free OH) was mechanically stirred in 50 g acetone (10% w / w) (400 rpm). It was dissolved at room temperature for 2 hours. Thereafter, the temperature of the system was raised to 56 ° C. When this temperature was reached, PA (0.25 or 0.75 PA: 1.0 polymer free OH, mol: mol) was added to the system. After dissolution (requires more than about 10 minutes of stirring), triethylamine (1.0 catalyst: 1.0 monoanhydride, mol: mol) as catalyst was added. The reaction was continued for 4 hours.

<Reaction of the product obtained in 3.1 with 3.2-dianhydride>
After reaction of cellulose acetate (CA) with monoanhydride (as described in 3.1), dianhydrides (0.5, 1.0 or predissolved in various solvents shown in Table 3 below) 2.0 Table 3 dianhydrides: initial polymer free OH before reaction with 1.0 monoanhydride, mol: mol) was added. After homogenization, triethylamine as catalyst (1.0 of catalyst: 1.0 of dianhydride, mol: mol) was added. The reaction was stopped when an increase in viscosity of the reaction system was observed (gel formation). Finally, the gel was washed with a water / ethanol solution 20% v / v and dried in an oven at 40 ° C. overnight.
Each dianhydride was dissolved in a different solvent according to Table 3 below.

<3.3 Purification step>
After gel synthesis, the gel was added to a water / ethanol solution (20% w / w) for purification. The time required for this step is about 30 days or until no unreacted reagent is observed (aromatic components (dianhydrides, monoanhydrides) were monitored by UV-visible spectroscopy). During this time, the water / ethanol solution was changed every two days.

<3.4 Insertion Penetration Step—Gel Treatment with Saturated Sodium Bicarbonate (NaHCO ₃ )>
First, a saturated solution of sodium bicarbonate (NaHCO ₃ ) was prepared. In a beaker containing 100 mL of sodium bicarbonate solution, 1 g of dry gel was added. This solution was mixed for 24 hours at room temperature. After this time, the gel was filtered and dried in a 40 ° C. oven overnight.

(Conclusion)
The results in Table 4 clearly show that the method of the present invention reaches an improved swelling ratio of the resulting polymer gel as compared to a method that does not involve treating the polymer gel with a bicarbonate solution. Yes. In addition, the results are improved when the first reaction of the polymer with monoanhydride is performed.

<II-Agricultural application test>
a) Sample preparation Prepare three tests in the greenhouse:
1. The first to use hydrogels marked with * in the above examples (Table 4)
2. 2. Use a commercial hydrogel based on potassium polyacrylate, and Third, a blank sample without hydrogel.
Three 10L pots are filled with soil and 8g hydrogel (if applicable) and 2L water is introduced 7 hours before transplanting the melon plant (Cucumis melo L.).

b) Irrigation Water was poured into each pot with water drops. Each pot received the same nutrient solution (for 1.000 L of solution): 170 g monopotassium phosphate, 800 g calcium nitrate; 300 g potassium nitrate; 120 g potassium sulfate; 250 g magnesium sulfate and 30 g Ferromix®.
The frequency of irrigation was as follows:
-0-6 days, every day-7-15 days, every 2 days-16-24 days, every day-25-32 days, 2 times per day-33- picking, 3 times per day.
The volume of water was selected to maintain 10% drainage and conductivity in the drainage below 4.0 dS m-1.

c) Evaluation Water production (kg / m ³ ) was calculated using the relationship between fruit production (fruit weight by the plant) and water consumption (m ³ ) by the plant.
The water consumption by the plant was calculated as the difference between the amount of water applied considering the proportion of 10% drainage for salinity management and the amount drained.
Both data (water production and water consumption) were statistical tests (Tukey-5% probability level).

d) Results The results of the tests are shown in Table 5 below.

e) Conclusion The present invention (Test 1) is at least equivalent in performance level to a commercially available polyacrylate product (Test 2) by:
The present invention (Test 1) and the commercial product (Test 2) result in a reduction in moisture and are statistically different from the situation without gel. There is no statistical difference between Solvay and commercial products.
-The material of the present invention is biodegradable.
There are no statistical differences in other properties between the present invention (Test 1) and the commercial product (Test 2).

Claims (15)

(A) adding a cyclic dianhydride to a solution containing a polymer containing a hydroxyl group in the presence of a catalyst;
(B) maintaining the solution of step (a) under conditions suitable for crosslinking of the hydrophilic polymer with a cyclic dianhydride, thereby forming a polymer gel;
(C) A method for producing a polymer gel, comprising a step of treating the polymer gel with an aqueous bicarbonate solution.   The method of claim 1, wherein the polymer comprising hydroxyl groups is selected from the group consisting of polysaccharides and their derivatives.   The polymers containing hydroxyl groups are cellulose, hemicellulose, cellulose acetate (mono, di, or tri, or a mixture thereof), cellulose propionate (mono, di, or tri, or a mixture thereof), carboxymethyl cellulose and their 3. A method according to claim 1 or 2 selected from the group consisting of a mixture.   The cyclic dianhydride includes pyromellitic dianhydride (PMDA), ethylenediaminetetraacetic acid dianhydride (EDTA), diethylenetriaminepentaacetic acid dianhydride (DTPA), 3,3 ′, 4,4′-bisphenyltetra. The carboxylic acid dianhydride (BPDA), pyromellitic acid diimide (PyDi), benzophenone-3,3 ', 4,4'-tetracarboxylic dianhydride, and mixtures thereof. The method of any one of -3.   The method according to claim 1, further comprising the step (a0) of adding a cyclic monoanhydride to a solution containing a polymer containing a hydroxyl group in the presence of a catalyst before the step (a).   The cyclic monoanhydrides include aliphatic anhydrides such as maleic anhydride and succinic anhydride, or aromatic anhydrides such as phthalic acid and 1,2,4-benzenetricarboxylic anhydride, and their 6. The method of claim 5, wherein the method is selected from the group consisting of a mixture.   The method according to claim 5 or 6, wherein the cyclic monoanhydride is phthalic anhydride.   The method according to claim 1, further comprising a step (d) of drying the polymer gel in the step (c).   9. The method according to any of claims 1 to 8, wherein the molar ratio of dianhydride per hydroxyl group of the polymer in the solution of step (a) is about 0.1 to 2 mol / mol.   The process according to any of claims 2 to 9, wherein the molar ratio of monoanhydride per hydroxyl group of the polymer in the solution of step (a0) is about 0.1 to 1 mol / mol.   The polymer gel manufactured by the method in any one of Claims 1-10.   12. The polymer hydrogel according to claim 11, wherein the polymer gel has a swelling ratio according to ASTM JIS K 7223-teaback method of at least about 10, preferably at least about 50, more preferably at least about 100. Comprising a polymer matrix containing polymer chains having hydroxy-pending groups;
A first portion of the hydroxy-pending group is substituted with a divalent hydrocarbon group that crosslinks the polymer chain to each other, and a second portion of the hydroxy-pending group is substituted with a monovalent hydrocarbon group; The polymer gel, wherein the divalent hydrocarbon group has a polar functional COOH or a salt thereof.   14. The polymer gel of claim 13, wherein the second portion of the hydroxy pending group is substituted with a monovalent hydrocarbon group, and the monovalent hydrocarbon group has a polar functional COOH or salt thereof.   Agricultural devices that control the release of water, nutrients or phytochemicals, devices for environmental remediation, absorbent products for personal and home hygiene, toys, change their size when in contact with water or aqueous solutions 17. A product comprising a polymer gel according to any of claims 11, 12, 15 or 16 selected from the group consisting of devices suitable for: